The protagonist, Katagura, is a veteran writer who has been blessed with a successful series but remains single. For the past month, he has been experiencing a trial period with a partner robot, and salesmen frequently visit his house to check on the situation. According to the salesmen, it is the "era of a hundred years of life", and in the future, everyone will need someone's assistance. As Katagura contemplates purchasing the partner robot, he begins to reevaluate his future life...

Kaijuu have appreared! Nayuna, a new high school transfer student, encounters one of these beasts and comes face to face with a girl she witnesses escaping from the stomach of a fallen monster. A few days after this event, Nayuna makes the decision to join the Monster Repulsion Division.